Eddyfi Blog Why Uniformity and Resolution in Eddy Current Array Probes Matter

The coils most commonly used in ECA probes are what we call "pancake coils", because they are actually small discs of wound copper wire. Considering their circular shape, it would be false to think the sensitivity zone corresponds to their full diameter. If there is a flaw on the edge of the coil, it could be missed or the signal amplitude might be such that an inspector or analyst could easily dismiss it-leaving behind a potential source of failure of the asset. Ideally, we aim to go no lower than 85%, depending on the application and target defect, of the maximum amplitude wherever the flaw is located. In the image below, the vertical dashed lines show the limits of the actual functional zone of sensitivity of the coil. To work around this, conventional eddy current systems were raster scanning the surface with a wide overlap to avoid a flaw falling in the low sensitivity zone. This method was proven to be effective, but it also increased inspection time considerably, and deployment was more complex and less efficient.